1. Field of the Invention
The present invention relates to a liquid crystal display panel and a method of driving this panel and, more particularly, to a correction driving method for a liquid crystal display panel which uses a thin film transistor (TFT) as a switching element for driving block-divided pixels and is time-sharingly driven, whereby a high luminance line for every block which is generated when this panel is driven at an inversion period of one horizontal period is eliminated.
2. Description of the Prior Art
In a conventional liquid crystal display panel (i.e., LCD panel) which uses a TFT as a switching element for driving block-divided pixels and is timesharingly driven, an active matrix circuit substrate necessary to drive and a TFT active matrix circuit substrate of a display section are constituted on the same substrate. FIG. 3 is a schematic arrangment diagram showing an example of such an LCD panel. As two fundamental circuits to matrix-drive a display section P, a gate line driver G and a source line driver D are arranged. Further, a block-dividing TFT array 1 is provided for a matrix circuit 2 from the source line driver D. The TFT array 1 is driven by a TFT array driver B. The portion surrounded by a broken line in the diagram, namely, the display section P, TFT array 1, and matrix circuit 2 are constituted on the same substrate.
FIG. 4 is a wiring diagram showing in further detail the portion on the same substrate mentioned above. In FIG. 4, output lines D.sub.1, D.sub.2, D.sub.3, . . . , D.sub.m from the source line driver D, which is the video output circuit, are combined as one block on an m-line unit basis of the output lines by the matrix circuit 2. When it is assumed that the number of blocks is k, (m.times.k) video signal lines are obtained due to the matrix of m.times.k. The respective blocks are combined to m video signal lines S.sub.1, S.sub.2, S.sub.3, . . . , S.sub.m by output lines B.sub.1, B.sub.2, . . . , B.sub.k from the TFT array driver B, respectively. The video signal lines S.sub.1 to S.sub.m are grounded through holding capacitors C. A pixel U of a liquid crystal cell indicated by O in the diagram is arranged in each cross point of the matrix consisting of the (m.times.k) video signal lines and output lines G.sub.1, . . . , G.sub.m-1, G.sub.m from the gate source driver G.
When the above-mentioned LCD panel is driven at the inversion period of one horizontal period, a charge shift phenomenon called a charge sharing effect occurs in the boundary portion between the divided blocks, namely, between the video signal lines S.sub.m and S.sub.1 in FIG. 4 due to the capacitive component between the source lines. Thus, a voltage of .DELTA.V as much as the amount of this effect is added to the video signal on the signal line S.sub.m and a signal of a voltage amplitude larger than the inherent video signal is outputted. (The opposite electrodes are grounded).
The principle of the charge sharing effect will then be described hereinbelow with reference to FIGS. 5 and 6. FIG. 5 is a principle diagram of the charge sharing effect and FIG. 6 is a time chart thereof. In FIG. 5, an alternate long and short dash line at the center of the diagram indicates a boundary between the blocks and the left hand of the alternate long and short dash line assumes the first block and the right hand assumes the second block. For the last signal line S.sub.m in the first block, an output from the last source line D.sub.m is driven by a first block driving voltage B.sub.1 by the block dividing TFT. For the first signal line S.sub.1 in the second block, an output of the first source line D.sub.1 is driven by a second block driving voltage B.sub.2 by the block dividing TFT. Source line capacitances C.sub.m and C.sub.l with respect to source terminals of the respective block dividing TFTs correspond to the video signal holding capacitor C. A capacitance C.sub.ss between the lines to cause the voltage .DELTA.V exists between the source lines. As shown in FIG. 6, when a gate pulse is inputted to B.sub.1, the video signal D.sub.m is transmitted to S.sub.m through the channel of the TFT, namely, it is charged in C.sub.m. After the source lines in the first block to which C.sub.m belongs have been completely charged, a pulse is then inputted to B.sub.2 and the source lines including S.sub.1 which belong to the second block are charged. At this time, charging waveforms of S.sub.m and S.sub.1 arranged in the boundary portion of two blocks change as shown in FIG. 6. The amplitude .DELTA.V which is indicated by the hatched portion in FIG. 6 is added to S.sub.m, so that S.sub.m is larger than the inherent video signal. On one hand, a waveform of S.sub.1 fluctuates as shown by the hatched portion in the diagram at the early time of inversion. Such a phenomenon occurs since the capacitance C.sub.ss between the source lines produces the charge sharing effect between C.sub.m and C.sub.l. The relation between .DELTA.V and V is approximated by the following expression (C=C.sub.m .apprxeq.C.sub.1) EQU V.apprxeq.C.sub.ss /C+C.sub.ss .multidot.V (.nu.)
When the foregoing LCD panel is driven without performing any correction, the last S.sub.m line is observed by the eyes as the high luminance line for every block, resulting in a fairly inconvenient as a display.